X-ray tube safety switch



July 21, 1942. E. R. GOLDFIELD X-RAY TUBE SAFETY SWITCH Filed Sept. 27, 1940 INVENTOR EDWIN R. GOLDFIELD f 401% ATTQRNEYS Patented July 21, 1942 5 X-RAY TUBE SAFETY SWITCH Edwin R. Goldfield, University Heights, Ohio, as-

signor to Picker X-Ray Corporation, Waite Manufacturing Division, Inc., Cleveland, Ohio, a corporation of Ohio Application September 27, 1940, Serial No. 358,602

3 Claims.

This invention relates to improvements in safety devices for preventing the overheating of X-ray tubes, and more particularly to a switch arranged to automatically cut off the tube circuit if the temperature of the tube rises above a predetermined point.

An object of the present invention is to disconnect the tube circuit by means of a device movable in response to tube temperature and which acts automatically so as to be in no way dependent upon the operator. This feature may be combined with -a signal device adapted to first signal the operator that excessive heat conditions have arisen so that he may complete the operation in which he is engaged before the automatic device deenergizes the tube. My invention contemplates any means for producing the desired results which comes within the purview of the appended claims but in the embodiment shown herein I have selected a fluid-tight housing for the X-ray tube filled with a fluid which is ex pansible when heated and have arranged an expansible diaphragm subject to the pressure of the fluid for actuating a switch in the tube control circuit. Other embodiments will occur to those skilled in this art.

In the drawing, Fig. 1 is a central longitudinal section through a typical X-ray tube and housing illustrating one means of practicing my invention; Fig. 2 is an enlarged sectional view of the apparatus at the left-hand end of Fig. 1; Fig. 3 is a plan view on reduced scale of a button retaining cup as viewed from the left-hand end of Fig. 2; while Fig. 4 is a diagrammatic view illustrating the place of my improved safety device in a tube control circuit.

In Fig. l I have shown an X-ray tube and its housing such as is disclosed in the copending application of Edward B. Graves, Serial No. 320,323, filed February 23, 1940, but it will be understood that this is in no sense a limitation but merely indicates one manner in which my invention may be applied to an X-ray tube.

In Fig. l the tube proper is indicated at I having an anode II which is connected to terminals I2 and having a cathode, not shown, which is connected to the terminals [3. The tube is encased in a fluid-tight housing l4 having the usual window opening at l5. The housing has tubular extensions l6 for receiving cable connections for the attachment of the energizing circuit to the terminals l2 and I3. As explained in the above mentioned copending application, the housing I4 is filled with an insulating oil or the like which expands and contracts in response to temperature changes within the housing M. It is usual to provide some sort of expansible diaphragm wall subject to the pressure in the housing which expands as the oil is heated so as to compensate and prevent undesirable rises of pressure within the housing. As shown in the ,ment circuit is indicated at L3, L4.

copending application but having no particular bearing here, I have indicated a fan at IT. driven by a motor H? which may be used to keep the oil in circulation, as explained in the copending application.

The present invention utilizes the movement of the expansible diaphragmlto automatically deenergize the tube upon an undesirable rise of temperature in the tube housing, such as would occur after unusually long or heavy demand upon the X-ray tube or upon some unforeseen failure or the like. My invention provides an automatic means for cutting off the current supply to the X-ray tube when it has generated an undue amount of heat. One embodiment of my invention as here shown makes use of an expansib'le and contractible bellows 19 such as has heretofore been used merely to compensate for changes in pressure within the housing I4. This bellows as shown in Fig. 2 has its left-hand end secured to the housing 14 and its right-hand end is sub jected to the pressure of the oil within the housing so that when the oil expands with a rising temperature, the right-hand end or bellows head [9a moves toward the left so as to contract the bellows. This of course relieves the pressure Within the housing and I utilize the movement of this bellows head to actuate a switch device 20 so as to deenergize the tube if the temperature within the housing has increased to an unusual degree.

For purposes of illustration I have used a standard tube circuit as shown in Fig. 4 to indicate one possible position of the switch 20 in such a circuit. The X-ray tube is indicated at In with a current supply at L1, L2 connected by means of an autotransformer 2| with the primary 22 of the transformer whose secondary 23's'upp1ies high tension current to the tube Ill. The fila- The usual disconnect switch is shown at 24 and in series therewith I have indicated the switch 20 which as mentioned before, I operate in response to temperature conditions of the X-ray tube. It will be obvious that when the switch 20 is opened the tube ill will be deenergized.

Referring back to Fig. 2, I have combined the safety switch with a device adapted to give a preliminary warning signal to the operator before the safety switch opens the tube circuit. In the form here shown a button 25 is movable in and out of an opening in the end of the housing M.

which it is held between the bellows and the end of the housing so as to fix the cup in place. A light spring 23 urges the button 25 inwardly. The outer portion of the button surface as indicated at 29 is of white or some other neutral color, whereas a portion of the surface 30 located inwardly therefrom may have a red band upon it so as to provide a warning when the button is moved out of the housing s'u'fiiciently to disclose the red band.

The switch 20 is of a known type, operable by means of relative longitudinal movement of the parts thereof, one part being associated with the button 25 and the other part with the bellows head |9a so that when movement of the button 25 outwardly is arrested by engagement of the parts 25a and 23 then furthermovement of the bellows head I901. toward the left as viewed in Figs. 1 and 2, will take up the lost motion of the switch and eventually throw the switch so as to open the tube circuit.

For purposes of understanding the operation of the present invention, I will explain the operation of the switch which, per se, is not my invention. An outer sleeve 3| carries at its righthand end a metal housing 32 within which is held a block of insulating material 33 which carries a pair of binding posts 34 located one behind the other in Fig. 2. To these binding posts are connected the wires 22a and 22b, the position of which will be understood from the diagram of Fig. 4. The binding posts 34 are electrically connected with spaced contacts located in the central cavity of the insulating block 33. A roller member 35 is adapted to make connection between these contacts when in the full line position of Fig. 2, whereas in the dot-dash position thereof the contact will be broken through the switch. A yieldable toggle device of known construction is utilized for snapping the contact member 35 over center. The toggle device includes a bell crank arm 35a, the other arm of which is indicated at 3517. The bell crank has a pivot at 31 which is a pin mounted in the sleeve 3|. An inner sleeve 38 is reciprocable within the sleeve 3| and carries at its right-hand end a slotted recess within which the arm 38b rests. A spring 39 is engaged between the left-hand end of sleeve 33 and a member 4|! which is held in position by the pin 31. Thus the'spring 39 tends to move sleeve 38 toward the left so as to normally return the switch parts to the full line position of Fig. 2 when pressure on the diaphragm head |9a is relieved.

The switch 2!] may be connected to the diaphragm head in any desired manner. As here shown a plate 4| is connected by a screw 32 with the diaphragm head and a U-shape strap 43 is secured by threaded washers to the outer face of sleeve 3|, the sides of the strap extending down to the member 4| on either side of block-33 and the saddle 43 being secured to the member 4|.

It results from the above construction that with the parts in the position of Fig. 2, the X-ray tube may be energized by closing the switch 24 because the switch 20 is in normal closed position as shown in full lines in Fig. 2. As the oil in the housing l4 expands with rising temperature of the tube, the diaphragm head |9a moves to ward the left pushing the entire switch 23 toward the left because the spring 39 is stronger'than the spring 28. The left-hand end of sleeve 38 thus pushes button 25 out of the housing until eventually the red band 30 is visible. This gives the operator warningthat the tube is becoming heated and that undue prolongation of the operation will result in an automatic shutdown. When the flange 26 engages flange 25a, limiting further outward movement of the button 25, further movement of the diaphragm head |9a toward the left causes relative sliding movement of the switch operating sleeves 3| and 38. This carries the bell crank arms 35a and 36b clock- *wise"about the pin 31 until the toggle switch throws over center, moving the roller contact 35 to the dot-dash position of Fig. 2' and opening the switch 20. This deenergizes the tube which must be left idle. for a period sufficient to permit the oil to contract within the housing l4 and permitting the diaphragm head I911. to move sufficiently toward the right to again cause the toggle switch to snap over center to the full line position of Fig. 2. In other words there is sufficient lost motion in switch 23 to give a warning period before the switch is opened and then to give a cooling period for the tube of a substantial time period. In other words the device does not flutter back and forth making and breaking the switch contacts rapidly.

It will be noted that the cable 44 housing the wires 22a and 22b is looped through several openings 45 in the cup 21 so as to establish a bight Ma in the cable, allowing for the longitudinal movement of the switch parts at all times.

What I claim is:

1. In the combination of an X-ray and a control circuit therefor, a fluid-tight housing for said tube, fluid in said housing expansible in response to temperature change, an expansible diaphragm'movable in response to fluid pressure in said housing, a warning signal device carried by said housing and movable relative thereto firstly to give a signal and secon'dlyto engage an abutment, a switch in said circuit'having relatively movable parts'for making ancl'breaking'the circuit, and one of said parts engaging said signal device and the other of said parts engaging said diaphragm in a manner to operate said switch when said signal. device is held. by said abutment and said diaphragm continues to move.

2. In the combination of an 'X-ray tube and a control circuit therefor, a fluid-tighthousing for said tube, fluid in said housing expansible in response to temperature change, an expansible diaphragm movable in response to fluid pressure in said housing, a toggle switch in said circuit, relatively movable parts connected with said diaphragm an'd with'said housing respectively, and saidparts'being operatively connected with said switch to move said toggle over center. to make and break said ."circuit upon relative movement of said parts, whereby when said circuit is broken at said switch, a cooling perio'dis necessary to contract said diaphragm sufficiently to move said toggle 'over center in switchclosing direction.

3. In the combination of an X-ray tube anda control circuittherefor, a part expansible by heat generated by said tube in operation, a, switch in said circuit, mean operatively connected with said expansible partfor controlling said switch including a spring loaded by movement of said expansible part, and said spring having anoperative connection'for throwinglsaid switch open when said spring is loadedfwhereby when said circuit is broken at said switch, a cooling period of said tube is necessary to provide return movement of said expansible part'sufiicient to permit closing of said switch.

EDWIN. R. GOLDFIELD. 

